An extruded AZ31 alloy was compressed along the extrusion direction at room temperature. Profuse tensile twins were activated. Paired twins including the connected twin pairs and randomly paired twins (unconnected twins) were studied by a combined analysis of Schmid factor and strain compatibility factor. The results show that the nucleation of connected twin pairs preferentially occurs in the neighboring grains with the misorientation of 25°. About 88% of the connected twins have high Schmid factor and around 76% show high strain compatibility factor. The occurrence of connected twin pairs with low values of Schmid factor is well interpreted by their high values of strain compatibility factor. Around 22% of the unconnected twin pairs have the strain compatibility factor values of zero.